The term section control refers to a technical system for the measurement of speeds of vehicles on road segments. Contrary to a standard speed trap, which measures the speed of a bypassing vehicle at a certain point (e.g. by means of a Doppler-radar), a section control system measures the average speed over a certain road-segment. It takes notice of the same vehicle passing two geographically distant points within a certain time. The known distance of the measurement devices, hereafter called roadside systems or gantries, in connection with the known travel time permits calculation of the average speed along the section of interest, and subsequent legal actions upon a speed limit violation.
When a section control system is implemented, particular care has to be taken regarding the protection of the identity of an observed vehicle's driver. In fact, the system must respect the driver's privacy up to the point when there is evidence of a speed limit violation. In particular, this means that the system should not store or process any personal data for purposes other than detecting a speed limit violation. Identities of drivers that behaved correctly should be protected at all times (i.e. neither be stored or processed any further).
Existing methods for section control (conf. e.g. EP 2 220 634, EP 2 360 647) rely on a comparison of hashed values of vehicle identifiers captured at the first and second roadside systems and, in case of a match, evaluating their clear-text timestamps to calculate travel time and thus the speed of the vehicle between the first and the second roadside systems. When a speed violation is detected, the vehicle identifiers captured at the outset have to be retrieved in the first and second roadside systems on the basis of the hashed values, which requires appropriate look-up tables for the captured evidence data.
The prior art systems are still inadequate regarding data protection and user privacy because the travel time of a vehicle is public, even when there is no speed violation, and because the originally captured evidence data stored in the roadside systems is prone to intruder attacks. There is therefore a need for methods for section control with improved security and privacy.